Ultraviolet curable silicone composition and cured product thereof

ABSTRACT

Provided are a low-viscosity ultraviolet curable silicone composition capable of being used even in a surface exposure method and a lift-up method etc.; and a cured product superior in tensile strength and elongation at break. The ultraviolet curable silicone composition contains:(A) an organopolysiloxane;(B) a photopolymerization initiator; and(C) a monofunctional (meth)acrylate compound having no siloxane structure and/or (D) a multifunctional (meth)acrylate compound having no siloxane structure, wherein the organopolysiloxane is represented by the following general formula (1):wherein n satisfies 1≤n≤1,000, m satisfies 1≤m≤1,000, Ar is an aromatic group, R1 represents a monovalent hydrocarbon group having 1 to 20 carbon atoms, A is a group represented by the following formula (2):wherein p satisfies 0≤p≤10, a satisfies 1≤a≤3, R1 represents a monovalent hydrocarbon group having 1 to 20 carbon atoms, R2 represents an oxygen atom or an alkylene group, R3 represents an acryloyloxyalkyl group or the like.

TECHNICAL FIELD

The present invention relates to an ultraviolet curable siliconecomposition and a cured product thereof.

BACKGROUND ART

In recent years, molding materials for use in 3D printers are beingdeveloped actively, and there exists various kinds of molding materialsincluding metal to resin-based materials. While acrylate photocurableresin compositions and urethane acrylate photocurable resin compositionshave been mainly employed in the field of resin, the cured products ofthese compositions are extremely hard and thus cannot be bended (Patentdocument 1).

Flexible materials are now required more often depending on intendeduses, and materials suitable for various molding methods have alreadybeen developed. For example, as a material intended forstereolithography (SLA), there has been developed a compositioncomprising an alkenyl group-containing organopolysiloxane, a mercaptogroup-containing organopolysiloxane and a MQ resin (Patent document 2).Further, there is also disclosed a platinum catalyst-containing siliconemixture that is intended for dispensing techniques and is capable ofbeing activated by ultraviolet rays (Patent document 3). Furthermore,there is disclosed a photocurable low-viscosity silicone materialintended for 3D printers employing inkjet methods (Patent document 4).However, the problem with such composition is that the cured productthereof is inferior to those of normal silicone materials in heatresistance. There has been a strong desire to develop a material notonly applicable to molding methods called surface exposure method andlift-up method which are methods that have seen a rapid increase innumbers in recent years, but also superior in heat resistance.

PRIOR ART DOCUMENTS Patent Documents

Patent document 1: JP-A-2012-111226

Patent document 2: Japanese Patent No. 4788863

Patent document 3: Japanese Patent No. 5384656

Patent document 4: WO2018/003381

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention was made in view of the aforementionedcircumstances, and it is an object of the present invention to provide alow-viscosity ultraviolet curable silicone composition capable of beingused even in a molding method such as a surface exposure method and alift-up method; and a cured product superior in heat resistance.

Means to Solve the Problems

After diligently conducting a series of studies to achieve theabovementioned object, the present invention was completed as follows.That is, it was found that a low-viscosity ultraviolet curable siliconecomposition and a cured product thereof with an excellent heatresistance could be provided by employing a particular ultravioletcurable organopolysiloxane component; and a monofunctional ethylenegroup-containing compound having no siloxane structure and/or amultifunctional ethylene group-containing compound having no siloxanestructure.

The present invention is to provide the following ultraviolet curablesilicone composition and a cured product thereof.

[1]

An ultraviolet curable silicone composition comprising:

(A) 100 parts by mass of an organopolysiloxane;

(B) 0.1 to 10 parts by mass of a photopolymerization initiator; and

1 to 400 parts by mass of at least one of (C) a monofunctional(meth)acrylate compound having no siloxane structure and (D) amultifunctional (meth)acrylate compound having no siloxane structure,wherein the organopolysiloxane is represented by the following generalformula (1):

wherein n is a number satisfying 1≤n≤1,000, m is a number satisfying1≤m≤1,000, siloxane units identified by n and m are sequenced in anyorder, Ar is an aromatic group, each R¹ independently represents amonovalent hydrocarbon group having 1 to 20 carbon atoms, A is a grouprepresented by the following formula (2):

wherein p is a number satisfying 0≤p≤10, a is a number satisfying 1≤a≤3,each R¹ independently represents a monovalent hydrocarbon group having 1to 20 carbon atoms, R² represents an oxygen atom or an alkylene group,R³ represents an acryloyloxyalkyl group, a methacryloyloxyalkyl group,an acryloyloxyalkyloxy group or a methacryloyloxyalkyloxy group.

[2]

The ultraviolet curable silicone composition according to [1], whereinR¹ in the general formula (1) represents an alkyl group having 1 to 10carbon atoms.

[3]

The ultraviolet curable silicone composition according to [1] or [2],wherein the ultraviolet curable silicone composition has a viscosity ofnot higher than 10,000 mPa·s at 25° C.

[4]

A cured product of the ultraviolet curable silicone compositionaccording to any one of [1] to [3].

[5]

The ultraviolet curable silicone composition according to any one of [1]to [3], wherein the ultraviolet curable silicone composition is for useas a 3D printer ink.

Effects of the Invention

Since the ultraviolet curable silicone composition of the presentinvention has such a low viscosity that it is even capable of being usedin a molding method such as a surface exposure method and a lift-upmethod, the composition is anticipated as a novel molding material foruse in 3D printers. Further, since the ultraviolet curable siliconecomposition of the present invention can be turned into a cured productsuperior in heat resistance, the composition is also anticipated as amolding material for use in 3D printers employing inkjet methods.

MODE FOR CARRYING OUT THE INVENTION

The present invention is described in greater detail hereunder.

(A) Organopolysiloxane

A component (A) is an organopolysiloxane represented by the followinggeneral formula (1).

In the formula (1), examples of an aromatic group represented by Arinclude aromatic hydrocarbon groups such as a phenyl group, a biphenylgroup and a naphthyl group; and hetero atom (O, S, N)-containingaromatic groups such as a furanyl group. Further, the aromatic grouprepresented by Ar may have a substituent group(s) such as a halogenatom(s) (e.g. chlorine atom, bromine atom, fluorine atom). It ispreferred that Ar be an unsubstituted aromatic hydrocarbon group,particularly preferably a phenyl group.

In the formula (1), n satisfies 1≤n≤1,000, preferably 1≤n≤500, morepreferably 1≤n≤400. When n is smaller than 1, volatilization will takeplace easily; when n is larger than 1,000, the composition will exhibita higher viscosity, which will then result in a poor handling property.

In the formula (1), m satisfies 1≤m≤1,000, preferably 1≤m≤500, morepreferably 1≤m≤400. When m is smaller than 1, volatilization will takeplace easily; when m is larger than 1,000, the composition will exhibita higher viscosity, which makes it difficult to perform molding via alift-up method.

In the formula (1), n+m satisfies 2≤n+m≤2,000, preferably 2≤n+m≤1,000,more preferably 2≤n+m≤800. When n+m is smaller than 2, volatilizationwill take place easily; when n+m is larger than 2,000, the compositionwill exhibit a higher viscosity, which makes it difficult to performmolding via a lift-up method.

In the formula (1), A represents a group expressed by the followingformula (2).

In the formulae (1) and (2), each R¹ independently represents amonovalent hydrocarbon group having 1 to 20 carbon atoms, preferably amonovalent hydrocarbon group having 1 to 10, more preferably 1 to 8carbon atoms, other than an aliphatic unsaturated group.

In the formulae (1) and (2), the monovalent hydrocarbon group having 1to 20 carbon atoms, as represented by R¹, may be linear, branched orcyclic, specific examples of which include alkyl groups such as a methylgroup, an ethyl group, an n-propyl group, an isopropyl group, an n-butylgroup, an isobutyl group, a tert-butyl group, an n-hexyl group, acyclohexyl group, an n-octyl group, a 2-ethylhexyl group and an n-decylgroup; alkenyl groups such as a vinyl group, an allyl(2-propenyl) group,a 1-propenyl group, an isopropenyl group and a butenyl group; arylgroups such as a phenyl group, a tolyl group, a xylyl group and anaphthyl group; and aralkyl groups such as a benzyl group, a phenylethylgroup and a phenylpropyl group.

Further, part of or all the carbon atom-bonded hydrogen atoms in any ofthese monovalent hydrocarbon groups may be substituted by othersubstituent groups; specific examples in such case includehalogen-substituted or cyano-substituted hydrocarbon groups such as achloromethyl group, a bromoethyl group, a trifluoropropyl group and acyanoethyl group.

Among the above examples, it is preferred that R¹ be an alkyl grouphaving 1 to 5 carbon atoms or a phenyl group, more preferably a methylgroup, an ethyl group or a phenyl group.

Further, in the formula (2), R² represents an oxygen atom or an alkylenegroup having 1 to 20, preferably 1 to 10, more preferably 1 to 5 carbonatoms.

In the formula (2), the alkylene group having 1 to 20 carbon atoms, asrepresented R², may be linear, branched or cyclic, specific examples ofwhich include a methylene group, an ethylene group, a propylene group, atrimethylene group, a tetramethylene group, an isobutylene group, apentamethylene group, a hexamethylene group, a heptamethylene group, anoctamethylene group, a nonamethylene group and a decylene group.

Among these examples, it is preferred that R² be an oxygen atom, amethylene group, an ethylene group or a trimethylene group, morepreferably an oxygen atom or an ethylene group.

Further, in the formula (3), each R³ independently represents anacryloyloxyalkyl group, a methacryloyloxyalkyl group, anacryloyloxyalkyloxy group or a methacryloyloxyalkyloxy group.

In the formula (3), there are no particular restrictions on the numberof the carbon atoms in the alkyl (alkylene) group(s) in theacryloyloxyalkyl group, methacryloyloxyalkyl group, acryloyloxyalkyloxygroup or methacryloyloxyalkyloxy group, as represented by R³. The numberof the carbon atoms in such alkyl (alkylene) group(s) is preferably 1 to10, more preferably 1 to 5. Specific examples of these alkyl groupsinclude those that are listed above as the examples of R¹, particularlythose having 1 to 10 carbon atoms.

Specific examples of R³ include, but are not limited to thoserepresented by the following formulae.

(In the above formulae, b represents a number satisfying 1≤b≤4; R⁴represents an alkylene group having 1 to 10 carbon atoms.)

In the above formula (2), p represents a number satisfying 0≤p≤10,preferably 0 or 1; a represents a number satisfying 1≤a≤3, preferably 1or 2.

As an example(s) of the organopolysiloxane represented by the formula(1), there may be listed the following compounds.

(In the above formulae, R¹, R², R⁴, Ar, n, m and b are defined as above;siloxane units identified by n and m are sequenced in any order.)

These organopolysiloxanes can be produced by known methods. Theorganopolysiloxane represented by the formula (3) may, for example, beobtained as a reactant of a hydrosilylation reaction between a both enddimethylvinylsiloxy group-blocked dimethyl siloxane-diphenylsiloxanecopolymer and 3-(1,1,3,3-tetramethyldisiloxanyl)propyl methacrylate (CASNo. 96474-12-3).

The organopolysiloxane represented by the formula (4) can be obtained byreacting 2-hydroxyethyl acrylate with a reactant of a hydrosilylationreaction between a both end dimethylvinylsiloxy group-blocked dimethylsiloxane-diphenylsiloxane copolymer and dichloromethylsilane.

(B) Photopolymerization Initiator

As a photopolymerization initiator (B), a known photopolymerizationinitiator can be used, examples of which include2,2-diethoxyacetophenone, 2,2-dimethoxy-1,2-diphenylethane-1-one(Irgacure 651 by BASF), 1-hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184by BASF), 2-hydroxy-2-methyl-1-phenyl-propane-1-one (Irgacure 1173 byBASF),2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl-2}-methyl-propane-1-one(Irgacure 127 by BASF), phenylglyoxylic acid methyl ester (Irgacure MBFby BASF), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one(Irgacure 907 by BASF),2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone (Irgacure 369by BASF), bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure819 by BASF), 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (IrgacureTPO by BASF) and mixtures of these compounds.

Among the above examples of the component (B), preferred are2,2-diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenyl-propane-1-one(Irgacure 1173 by BASF), bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (Irgacure 819 by BASF) and2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (Irgacure TPO by BASF)in terms of compatibility to the component (A)

The photopolymerization initiator is added in an amount of 0.1 to 10parts by mass per 100 parts by mass of the component (A). A curedproduct will exhibit an insufficient curability when thephotopolymerization initiator is added in an amount of smaller than 0.1parts by mass; the cured product will exhibit a poor depth-curabilitywhen the photopolymerization initiator is added in an amount of greaterthan 10 parts by mass.

(C) Monofunctional (Meth)Acrylate Compound Having No Siloxane Structure

Examples of (C) a monofunctional (meth)acrylate compound having nosiloxane structure, include isoamyl acrylate, lauryl acrylate, stearylacrylate, ethoxy-diethylene glycol acrylate, methoxy-triethylene glycolacrylate, 2-ethylhexyl-diglycol acrylate, phenoxyethyl acrylate,phenoxydiethylene glycol acrylate, tetrahydrofurfuryl acrylate,isobornyl acrylate and mixtures of these compounds; isobornyl acrylateis particularly preferred.

(D) Multifunctional (Meth)Acrylate Compound Having No Siloxane Structure

Examples of (D) a multifunctional (meth)acrylate compound having nosiloxane structure, include triethyleneglycol diacrylate,polytetramethylene glycol diacrylate, neopentylglycol diacrylate,1,6-hexanediol diacrylate, dimethylol-tricyclodecane diacrylate,trimethylolpropane triacrylate, pentaerythritol tetraacrylate andmixtures of these compounds; dimethylol-tricyclodecane diacrylate isparticularly preferred.

It is preferred that the (meth)acrylate compounds as the components (C)and (D) be contained in a total amount of 1 to 400 parts by mass, morepreferably 1 to 200 parts by mass, per 100 parts by mass of thecomponent (A). When the components (C) and (D) are added in a totalamount of greater than 400 parts by mass per 100 parts by mass of thecomponent (A), the cured product will exhibit an unnecessarily highhardness, which may make it impossible to achieve desired rubberproperties.

Additives such as a silane coupling agent, a polymerization inhibitor,an antioxidant, an ultraviolet absorber as a light-resistant stabilizer,and a light stabilizer may be further added to the composition of thepresent invention without impairing the effects of the presentinvention. Further, the composition of the present invention may beappropriately mixed with other resin composition(s) before use.

Method for Producing Silicone Composition

The ultraviolet curable silicone composition of the present invention isobtained by, for example, stirring and mixing the components (A), (B),(C) and/or (D) as well as other components. Although there are noparticular restrictions on a device for performing stirring or the like,a planetary mixer and a separable flask may, for example, be used.

In the case of the ultraviolet curable silicone composition of thepresent invention, as a guide for enabling molding via a lift-up method,it is preferred that the composition have a viscosity of 10 to 10,000mPa·s, more preferably 100 to 8,000 mPa·s. Here, such viscosity is avalue measured at 25° C., using a rotary viscometer.

The ultraviolet curable silicone composition of the present inventioncures rapidly when irradiated with ultraviolet rays. As a light sourceof the ultraviolet rays with which the ultraviolet curable siliconecomposition of the present invention is to be irradiated, there may beused, for example, a UVLED lamp, a high-pressure mercury lamp, a superhigh-pressure mercury lamp, a metal halide lamp, a carbon-arc lamp or axenon lamp. An irradiance level (integrated light quantity) of theultraviolet rays is such that when, for example, the composition of thepresent invention has been formed into a sheet having a thickness ofabout 2.0 mm, the irradiance level is preferably 1 to 10,000 mJ/cm²,more preferably 10 to 5,000 mJ/cm². That is, when employing anultraviolet ray of an illuminance of 100 mW/cm² (365 nm), irradiationmay simply be carried out for about 0.01 to 100 sec using suchultraviolet ray.

Further, in order for the cured product of the ultraviolet curablesilicone composition of the present invention to exhibit superior rubberproperties, a hardness after curing is in a range of 5 to 80 (Type A),preferably a range of 10 to 70 (Type A). It is preferred that a tensilestrength after curing be not lower than 0.6 MPa, more preferably notlower than 0.8 MPa. It is preferred that an elongation at break aftercuring be not lower than 40%, more preferably not lower than 50%. Here,these values are measured in accordance with JIS-K6249. The rubberproperties of the cured product can be adjusted by increasing ordecreasing the amount of the components (C) and (D) added.

WORKING EXAMPLES

The present invention is described in detail hereunder with reference toworking and comparative examples. However, the present invention is notlimited to the following working examples.

Working Examples 1 to 4; Comparative Example 1

An ultraviolet curable silicone composition was obtained by mixing thefollowing components at the compounding ratios shown in Table 1 (valuesrepresent parts by mass).

Here, the viscosity of the composition obtained in each example is avalue measured by a rotary viscometer at 25° C.

Further, each composition was poured into a frame, followed by using alamp, H(M) 06-L-61 manufactured by EYE GRAPHICS Co., Ltd. to cure thecomposition under a nitrogen atmosphere and an ultraviolet rayirradiation condition of 2,000 mJ/cm², thereby obtaining a cured sheeteach having a thickness of 2.0 mm. As for each cured sheet, a hardness,a tensile strength and an elongation at break thereof before and after aheat resistance test (left at 200° C. for 20 hours) were measured inaccordance with JIS-K6249, and the measurement results are shown inTable 1.

Component (A)

(A-1): Organopolysiloxane produced by the abovementioned method andrepresented by the following formula (5)

(In this formula, siloxane units expressed with parentheses aresequenced in any order.)

(A-2): Organopolysiloxane produced by the abovementioned method andrepresented by the following formula (6)

(In this formula, siloxane units expressed with parentheses aresequenced in any order.)

(Comparative Component)

(A-3): Organopolysiloxane represented by the following formula (7)

(A-4): Organopolysiloxane represented by the following formula (8)

Component (B)

(B-1): 2-hydroxy-2-methyl-1-phenyl-propane-1-one (Irgacure 1173 by BASF)

(B-2): 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (Irgacure TPO byBASF)

Component (C)

Isobornyl acrylate (Light acrylate IB-XA by Kyoeisha Chemical Co., Ltd.)

Component (D)

Dimethylol-tricyclodecane diacrylate (Light acrylate DCP-A by KyoeishaChemical Co., Ltd.)

TABLE 1 Working Working Working Working Comparative example 1 example 2example 3 example 4 example 1 (A - 1) 100 100 — — — (A - 2) — — 100 100— (A - 3) — — — — 100 (A - 4) — — — — 75 (B - 1) 1.5 1.1 0.6 0.7 4.0(B - 2) 1.5 1.1 0.6 0.7 4.0 (C) 45 — 25 45 75 (D) — 10 — — — Compositionviscosity (mPa · s) 780 2870 530 360 60 Initial hardness (Type A) 29 4130 54 25 Initial tensile strength (MPa) 2.3 0.9 1.8 6.2 1.2 Initialelongation at break (%) 240 66 180 250 170 Hardness after heatresistance test 31 45 34 58 30 (Type A) Tensile strength after heat 2.21.0 2.1 4.6 0.4 resistance test (MPa) Elongation at break after heat 20050 150 190 30 resistance test (%)

As shown in Table 1, the ultraviolet curable silicone composition of thepresent invention has a sufficiently low viscosity, exhibits excellentrubber properties and heat resistance after curing, and is particularlyuseful as a silicone material intended for 3D printers employing moldingmethods such as a surface exposure method and a lift-up method. Incontrast, a cured sheet obtained in a comparative example 1 in which thecomponent (A) was not used was inferior in rubber properties after heatresistance test.

1. An ultraviolet curable silicone composition comprising: (A) 100 partsby mass of an organopolysiloxane; (B) 0.1 to 10 parts by mass of aphotopolymerization initiator; and 1 to 400 parts by mass of at leastone of (C) a monofunctional (meth)acrylate compound having no siloxanestructure and (D) a multifunctional (meth)acrylate compound having nosiloxane structure, wherein the organopolysiloxane is represented by thefollowing general formula (1):

wherein n is a number satisfying 1≤n≤1,000, m is a number satisfying1≤m≤1,000, siloxane units identified by n and m are sequenced in anyorder, Ar is an aromatic group, each R¹ independently represents amonovalent hydrocarbon group having 1 to 20 carbon atoms, A is a grouprepresented by the following formula (2):

wherein p is a number satisfying 0≤p≤10, a is a number satisfying 1≤a≤3,each R¹ independently represents a monovalent hydrocarbon group having 1to 20 carbon atoms, R² represents an oxygen atom or an alkylene group,R³ represents an acryloyloxyalkyl group, a methacryloyloxyalkyl group,an acryloyloxyalkyloxy group or a methacryloyloxyalkyloxy group.
 2. Theultraviolet curable silicone composition according to claim 1, whereinR¹ in the general formula (1) represents an alkyl group having 1 to 10carbon atoms.
 3. The ultraviolet curable silicone composition accordingto claim 1, wherein the ultraviolet curable silicone composition has aviscosity of not higher than 10,000 mPa·s at 25° C.
 4. A cured productof the ultraviolet curable silicone composition according to claim
 1. 5.(canceled)
 6. The ultraviolet curable silicone composition according toclaim 2, wherein the ultraviolet curable silicone composition has aviscosity of not higher than 10,000 mPa·s at 25° C.
 7. A cured productof the ultraviolet curable silicone composition according to claim
 2. 8.A cured product of the ultraviolet curable silicone compositionaccording to claim
 3. 9. A cured product of the ultraviolet curablesilicone composition according to claim 6.